/*
 *  kernel/sched/cpudl.c
 *
 *  Global CPU deadline management
 *
 *  Author: Juri Lelli <j.lelli@sssup.it>
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; version 2
 *  of the License.
 */
#include "sched.h"

static inline int parent(int i)
{
    return (i - 1) >> 1;
}

static inline int left_child(int i)
{
    return (i << 1) + 1;
}

static inline int right_child(int i)
{
    return (i << 1) + 2;
}

static void cpudl_heapify_down(struct cpudl *cp, int idx)
{
    int l, r, largest;

    int orig_cpu = cp->elements[idx].cpu;
    u64 orig_dl = cp->elements[idx].dl;

    if (left_child(idx) >= cp->size)
        return;

    /* adapted from lib/prio_heap.c */
    while (1) {
        u64 largest_dl;

        l = left_child(idx);
        r = right_child(idx);
        largest = idx;
        largest_dl = orig_dl;

        if ((l < cp->size) && dl_time_before(orig_dl,
                        cp->elements[l].dl)) {
            largest = l;
            largest_dl = cp->elements[l].dl;
        }
        if ((r < cp->size) && dl_time_before(largest_dl,
                        cp->elements[r].dl))
            largest = r;

        if (largest == idx)
            break;

        /* pull largest child onto idx */
        cp->elements[idx].cpu = cp->elements[largest].cpu;
        cp->elements[idx].dl = cp->elements[largest].dl;
        cp->elements[cp->elements[idx].cpu].idx = idx;
        idx = largest;
    }
    /* actual push down of saved original values orig_* */
    cp->elements[idx].cpu = orig_cpu;
    cp->elements[idx].dl = orig_dl;
    cp->elements[cp->elements[idx].cpu].idx = idx;
}

static void cpudl_heapify_up(struct cpudl *cp, int idx)
{
    int p;

    int orig_cpu = cp->elements[idx].cpu;
    u64 orig_dl = cp->elements[idx].dl;

    if (idx == 0)
        return;

    do {
        p = parent(idx);
        if (dl_time_before(orig_dl, cp->elements[p].dl))
            break;
        /* pull parent onto idx */
        cp->elements[idx].cpu = cp->elements[p].cpu;
        cp->elements[idx].dl = cp->elements[p].dl;
        cp->elements[cp->elements[idx].cpu].idx = idx;
        idx = p;
    } while (idx != 0);
    /* actual push up of saved original values orig_* */
    cp->elements[idx].cpu = orig_cpu;
    cp->elements[idx].dl = orig_dl;
    cp->elements[cp->elements[idx].cpu].idx = idx;
}

static void cpudl_heapify(struct cpudl *cp, int idx)
{
    if (idx > 0 && dl_time_before(cp->elements[parent(idx)].dl,
                cp->elements[idx].dl))
        cpudl_heapify_up(cp, idx);
    else
        cpudl_heapify_down(cp, idx);
}

static inline int cpudl_maximum(struct cpudl *cp)
{
    return cp->elements[0].cpu;
}

/*
 * cpudl_find - find the best (later-dl) CPU in the system
 * @cp: the cpudl max-heap context
 * @p: the task
 * @later_mask: a mask to fill in with the selected CPUs (or NULL)
 *
 * Returns: int - CPUs were found
 */
int cpudl_find(struct cpudl *cp, struct task_struct *p,
           struct cpumask *later_mask)
{
    const struct sched_dl_entity *dl_se = &p->dl;

    if (later_mask &&
        cpumask_and(later_mask, &cp->free_cpus, &p->cpus_allowed)) {
        return 1;
    } else {
        int best_cpu = cpudl_maximum(cp);

        WARN_ON(best_cpu != -1 && !cpu_online(best_cpu));

        if (cpumask_test_cpu(best_cpu, &p->cpus_allowed) &&
            dl_time_before(dl_se->deadline, cp->elements[0].dl)) {
            if (later_mask)
                cpumask_set_cpu(best_cpu, later_mask);

            return 1;
        }
    }
    return 0;
}

/*
 * cpudl_clear - remove a CPU from the cpudl max-heap
 * @cp: the cpudl max-heap context
 * @cpu: the target CPU
 *
 * Notes: assumes cpu_rq(cpu)->lock is locked
 *
 * Returns: (void)
 */
void cpudl_clear(struct cpudl *cp, int cpu)
{
    int old_idx, new_cpu;
    unsigned long flags;

    WARN_ON(!cpu_online(cpu));

    raw_spin_lock_irqsave(&cp->lock, flags);

    old_idx = cp->elements[cpu].idx;
    if (old_idx == IDX_INVALID) {
        /*
         * Nothing to remove if old_idx was invalid.
         * This could happen if a rq_offline_dl is
         * called for a CPU without -dl tasks running.
         */
    } else {
        new_cpu = cp->elements[cp->size - 1].cpu;
        cp->elements[old_idx].dl = cp->elements[cp->size - 1].dl;
        cp->elements[old_idx].cpu = new_cpu;
        cp->size--;
        cp->elements[new_cpu].idx = old_idx;
        cp->elements[cpu].idx = IDX_INVALID;
        cpudl_heapify(cp, old_idx);

        cpumask_set_cpu(cpu, &cp->free_cpus);
    }
    raw_spin_unlock_irqrestore(&cp->lock, flags);
}

/*
 * cpudl_set - update the cpudl max-heap
 * @cp: the cpudl max-heap context
 * @cpu: the target CPU
 * @dl: the new earliest deadline for this CPU
 *
 * Notes: assumes cpu_rq(cpu)->lock is locked
 *
 * Returns: (void)
 */
void cpudl_set(struct cpudl *cp, int cpu, u64 dl)
{
    int old_idx;
    unsigned long flags;

    WARN_ON(!cpu_online(cpu));

    raw_spin_lock_irqsave(&cp->lock, flags);

    old_idx = cp->elements[cpu].idx;
    if (old_idx == IDX_INVALID) {
        int new_idx = cp->size++;

        cp->elements[new_idx].dl = dl;
        cp->elements[new_idx].cpu = cpu;
        cp->elements[cpu].idx = new_idx;
        cpudl_heapify_up(cp, new_idx);
        cpumask_clear_cpu(cpu, &cp->free_cpus);
    } else {
        cp->elements[old_idx].dl = dl;
        cpudl_heapify(cp, old_idx);
    }

    raw_spin_unlock_irqrestore(&cp->lock, flags);
}

/*
 * cpudl_set_freecpu - Set the cpudl.free_cpus
 * @cp: the cpudl max-heap context
 * @cpu: rd attached CPU
 */
void cpudl_set_freecpu(struct cpudl *cp, int cpu)
{
    cpumask_set_cpu(cpu, &cp->free_cpus);
}

/*
 * cpudl_clear_freecpu - Clear the cpudl.free_cpus
 * @cp: the cpudl max-heap context
 * @cpu: rd attached CPU
 */
void cpudl_clear_freecpu(struct cpudl *cp, int cpu)
{
    cpumask_clear_cpu(cpu, &cp->free_cpus);
}

/*
 * cpudl_init - initialize the cpudl structure
 * @cp: the cpudl max-heap context
 */
int cpudl_init(struct cpudl *cp)
{
    int i;

    raw_spin_lock_init(&cp->lock);
    cp->size = 0;

    cp->elements = kcalloc(nr_cpu_ids,
                   sizeof(struct cpudl_item),
                   GFP_KERNEL);
    if (!cp->elements)
        return -ENOMEM;

    cpumask_clear(&cp->free_cpus);

    for_each_possible_cpu(i)
        cp->elements[i].idx = IDX_INVALID;

    return 0;
}

/*
 * cpudl_cleanup - clean up the cpudl structure
 * @cp: the cpudl max-heap context
 */
void cpudl_cleanup(struct cpudl *cp)
{
    kfree(cp->elements);
}
